The present invention relates to an anti-static anti-reflective film which is suitable for use in displays such as liquid crystal displays (LCDs), plasma displays (PDPs), CRTs, ELs, etc., and in particular, relates to an anti-static anti-reflective film exhibiting superior anti-reflective property, abrasion resistance, and anti-static properties.
Displays typified by LCDs, PDPs, CRTs, and ELs are widely used in various fields such as television and computer technologies, and have been developed rapidly. In particular, LCDs are in remarkably common use in note-book-type personal computers and word processors, portable telephones, PHSs, various portable terminals, etc., as displays which are thin, light, and extremely versatile.
In the past, in such displays, although an anti-reflective layer having a low refractive index had been formed to prevent reflection on the surface, there was a problem in that contamination such as dust, etc., adhered by static electricity occurring on the surface, since an insulating resin is generally used in the anti-reflective layer or other members constituting the display. As methods for preventing static electricity on the surface of the display, specifically, a method in which an anti-static layer is formed by depositing or sputtering an extremely thin layer of a metal oxide such as ITO or a metal such as aluminum or tin; by dispersing whiskers and metal microparticles such as those of aluminum or tin, whiskers and microparticles such as those of antimony-doped metal oxide such as tin oxide, fillerized charge-transfer complexes produced between 7,7,8,8-tetracyanoxydimethane and an electron donor such as an organic cation or a metal ion in a polyester resin, an acrylic resin, an epoxy resin, or the like, and subsequently solvent-coating; by solvent-coating a camphor-sulfonic-acid-doped polypyrrol, polyaniline, etc.; or a method in which an anti-reflective layer or another layer having an anti-static property is formed by containing the above anti-static materials therein, were typically used.
However, since the above anti-static fine particles and anti-static agents are materials having a very high refractive index, the refractive index of an anti-static layer or a layer containing the anti-static agent is increased, and therefore there was a problem in that the anti-reflective property thereof was deteriorated. Additionally, there was also a problem in that deterioration of abrasion resistance on the layer occurs due to the containing of such anti-static fine particles or anti-static agents.
The present invention has been made in view of the above circumstances, and it is an object thereof to provide an anti-static anti-reflective film which exhibits not only superior optical properties and physical properties but also superior anti-static properties.
The inventor has conducted various research with respect to anti-static properties on the mostsurface of an anti-reflective film in order to prevent static electricity occurring on the surface of displays, etc., and consequently, he has found that a superior anti-static property of the film can be exhibited by containing cation-modified silicon compounds in a low refractive layer while conventional superior optical properties and physical properties are maintained.
Therefore, an anti-static anti-reflective film according to the present invention is characterized in that a low reflective layer is provided on the surface of a transparent substrate directly or via another layer, the low reflective layer is formed by curing at least a silicon compound, and the silicon compound includes cation-modified silicon compounds.
In the following, preferable embodiments of an anti-static anti-reflective film of the present invention will be explained in detail.
A. Transparent Substrate
As a transparent substrate employed in an anti-static anti-reflective film according to the present invention, a conventional transparent film, glass, etc., can be employed. Specifically, various resin films such as polyethylene terephthalate (PET), triacetyl cellulose (TAC), polyacrylate, polyimide, polyether, polycarbonate, polysulfone, polyether sulfone, cellophane, aromatic polyamide, polyethylene, polypropylene, polyvinyl alcohol, and the like, and glass based materials such as fused glass, soda glass, and the like can be preferably employed. For PDPs and LCDs, PET and TAC are preferred.
The higher the transparency of the transparent substrate, the better the transparent substrate. The light transmittance (Japanese Industrial Standard C-6714) is preferably 80% or more, and is more preferably 90% or more. In the case in which the transparent substrate is employed in a compact and light-weight liquid-crystal display, the transparent substrate is preferably in the form of a film. It is desirable that the transparent substrate be thin from the standpoint of being light-weight, and it is preferred that the thickness of the transparent substrate be preferably 10 to 500 xcexcm in consideration of the productivity thereof.
In addition, the adhesion between the low reflective layer or another layer provided thereunder and the transparent substrate can be improved by surface-treatment of the transparent substrate such as an alkaline treatment, corona treatment, plasma treatment, fluorine treatment, sputtering treatment, or the like, a coating, on the transparent substrate, of a surface active agent, a silane coupling agent, or the like, or a surface-modification-treatment such as a Si deposition or the like.
B. Low Reflective Layer
A low reflective layer of the present invention is formed by curing at least a silicon compound, and preferably by curing a silica sol. The silica sol is a sol in which silica microparticles are dispersed in water or an organic solvent, and is produced by a method for condensation of an activated silicic acid which de-alkalizes an alkali metal ion in an alkaline salt of silicic acid by ion exchange, etc., or which neutralizes an alkaline salt of silicic acid with a mineral acid, or by a method for hydrolysis and condensation of an alkoxysilane in an organic solvent in the presence of a basic catalyst. Alternatively, an organic-solvent type silica sol (organosilica sol) obtained by replacing the water in an aqueous silica sol described above with an organic solvent by a distillation method may be employed. These silica sols can be employed in either an aqueous or organic-solvent condition. It is not necessary to completely replace the water with the organic solvent in the case of production of the organic-solvent type silica sol. The silica sol contains a solid component as SiO2 in a concentration of 0.5 to 50% by weight. Various types of silica ultra-microparticles in the silica sol, such as in a spheroidal form, a needle form, a plate form, or the like can be employed.
In addition, it is desirable that the pH be nearly neutral in consideration of dispersiveness to solvent, etc., since the silica sol is generally used by dispersing in organic solvent. The particle size of the silica sol is preferably 5 to 500 nm, and is more preferably 5 to 300 nm. When the particle size of the silica sol is below 5 nm, a reduction of the reflective characteristics can be insufficiently obtained. In contrast, when the particle size of the silica sol exceeds 500 nm, the haze value is increased and the surface of the film is hazy white, and in addition, the anti-static property is undesirable.
In addition, in the silicon compound in the present invention, a cation-modified silicon compound which works as a film forming agent and an anti-static agent must be contained. Furthermore, it is preferable that this cation-modified silicon compound contain nitrogen, and in particular, that nitrogen be contained as a quarternary ammonium salt. Specifically, as a cation-modified silicon compound, octadecyl dimethyl [3-(trimethoxysilyl) propyl] ammonium chloride, N-(3-trimethoxysilylpropyl)-N-methyl-N,N-diallyl ammonium chloride, N,N-didecyl-N-methyl-N-(3-trimethoxysilylpropyl) ammonium chloride, octadecyl dimethyl (3-trimethoxysilylpropyl) ammonium chloride, tetradecyl dimethyl (3-trimethoxysilylpropyl) ammonium chloride, N-trimethoxysilylpropyl-N,N,N-tri-n-butyl ammonium chloride, N-trimethoxysilylpropyl-N,N,N-trimethyl ammonium chloride, trimethoxysilylpropyl (polyethyleneimine), dimethoxymethylsilylpropyl modified (polyethyleneimine), etc., can be mentioned.
It is preferable that the cation-modified silicon compound in the present invention be a compound containing a nitrogen atom as a quarternary ammonium salt, because it is stable and handling thereof is easy. In addition, it is preferable that the cation-modified silicon compound in the present invention be employed so that the nitrogen content in a low reflective layer is 0.5 to 2.0% by weight, and more preferably 0.8 to 1.8% by weight, since there is a problem in which the containing of the nitrogen atom increases the refractive index, and therefore, the anti-reflection property is deteriorated. When the nitrogen content is below 0.5% by weight, the content of the quarternary ammonium salt is low, and the anti-static property is not sufficiently exhibited. In contrast, when the nitrogen content exceeds 2.0% by weight, there is a problem in that the anti-reflective property is deteriorated, and the abrasion resistance and water resistance are decreased.
Furthermore, it is preferable that the silicon compound in the present invention contain a fluorine-modified silicon compound as a film forming agent, because the anti-reflective property and abrasion resistance are improved. As a fluorine-modified silicon compound, trifluoropropyl trimethoxysilane, trifluoropropyl triethoxysilane, tridecafluorooctyl trimethoxysilane, tridecafluorooctyl triethoxysilane, heptadecafluorodecyl trimethoxysilane, heptadecafluorodecyl triethoxysilane, etc., can be mentioned. These can be employed alone or in combination. In addition, it is preferable that the content of fluorine-modified silicon compound be employed so that the ratio of fluorine atoms to silicon atoms (F/Si) in the silicon compound for forming a low reflective layer is 1.0 to 7.5, and more preferably 2.5 to 6.5.
The low reflective layer according to the present invention can be obtained, for example, by diluting the silicon compounds described above with a solvent, applying the silicon compounds directly on the substrate or via another layer by means of a spin coater, a roll coater, a printer, or the like, drying them at 50 to 80xc2x0 C., and curing them by heating at 100 to 500xc2x0 C. In the case in which, in the transparent substrate, a plastic film such as one of PET, TAC, or the like, which is liable to be damaged by heat, is employed, it is preferable that the heat-curing temperature be set low within a range not having a deleterious influence on the plastic film.
The thickness of the low reflective layer for exhibiting superior anti-reflective properties can be calculated according to a well-known expression. According to a well-known document (Science Library, Physics 9 xe2x80x9cOpticsxe2x80x9d, pp. 70 to 72), when incident light is transmitted vertically to a low reflective layer, it is considered that the conditions for which the low reflective layer does not reflect the light and for which the light is transmitted at 100% will be satisfied in the following relational expression. In the expression, N0 is the refractive index of the low reflective layer, NS is the refractive index of the substrate or an under layer on the substrate side, h is the thickness of the low reflective layer, and xcex0 is the wavelength of the light.
N0=NSxc2xdxe2x80x83xe2x80x83Expression(1) 
N0h=xcex0/4xe2x80x83xe2x80x83Expression(2) 
According to Expression (1), it can be seen that in order to prevent the light reflection completely (100%), a material wherein the refractive index of the low reflective layer corresponds to the square root of the refractive index of the substrate or the lower layer may be selected. In practice, it is difficult to find a material that satisfies the expression exactly, and therefore, a material which has properties very similar to those of a material that satisfies the expression exactly is used. In expression (2), the optimum thickness as an anti-reflective film of the low reflective layer can be calculated from the refractive index of the low reflective layer selected according to expression (1) and the wavelength of the light. For example, in the case where the refractive index of the substrate or the under layer and that of the low reflective layer are 1.50 and 1.38, respectively, and the wavelength of the light is 550 nm, an optical film thickness of the low reflective layer is calculated as approximately 0.1 xcexcm, and is preferably in a range of 0.1xc2x10.01 xcexcm, according to expression (2).
C. Other Layers
In the present invention, the above transparent substrate, and low reflective layer are the basic composition, and in addition, a hard coat layer, an anti-glare layer, etc., can be provided between the substrate and the low reflective layer by laminating as necessary. In the following, these are explained.
{circle around (1)} Hard Coat Layer
As a resin for forming a hard coat layer, resins for a hard coating can be employed. In the present invention, a xe2x80x9chard coatxe2x80x9d refers to one having a pencil hardness of H or more described in the following. As the resin, a resin cured by means of radiation or heat, or a combination thereof, can be employed. As a radiation curable resin, compounds appropriately mixed with monomers, oligomers, or prepolymers having polymeric unsaturated bonds such as for an acryloyl group, methacryloyl group, acryloyloxy group, methacryloyloxy group, or the like, can be employed. As a monomer, acrylic acid derivatives of monofunctional acrylates such as methyl acrylate, lauryl acrylate, ethoxy diethylene glycol acrylate, methoxy triethyleneglycol acrylate, phenoxy ethylacrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxy acrylate, or the like; and of multifunctional acrylates such as neopentylglycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane acrylic acid benzoate, trimethylolpropane benzoate, or the like; methacrylic acid derivatives of monofunctional methacrylate such as methyl methacrylate, 2-ethylhexyl methacrylate, n-stearyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, phenoxyethyl methacrylate, methoxy polyethylene methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxybutyl methacrylate, etc.; and of multifunctional methacrylates such as 1,6-hexanediol dimethacrylate, trimethylolpropane trimethacrylate, glycerol dimethacrylate, ethylene glycol dimethacrylate, or the like; a urethane acrylate such as glycerin dimethacrylate hexamethylene diisocyanate, pentaerythritol triacrylate hexamethylene diisocyanate, or the like; can be mentioned. As an oligomer or prepolymer, an acrylate such as polyester acrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate, alkyd acrylate, melamine acrylate, silicone acrylate, or the like, an unsaturated polyester, an epoxy-type compound, or the like, can be mentioned. These can be employed alone or in combination. In the case in which flexibility of the curing film is required, the amount of monomer employed is reduced. Furthermore, in order to reduce cross-linking density, it is preferable that an acrylic monomer having a mono-functional or bi-functional acrylate be employed. Whereas in the case in which superior durability such as thermal resistance, abrasion resistance, solvent resistance, or the like, is required in the curing film, it is preferable that the amount of the monomer be increased or that an acrylic monomer having a tri-functional or greater acrylate be employed.
In order to cure the radiation curable resin as described above, for example, it is necessary that radiation such as UV, electron beams, X-rays, or the like, be irradiated on the resin, and a polymerization initiator can be appropriately added to the resin, as necessary. In the case of curing by means of irradiating with UV, a photopolymerization initiator must be added. As a photopolymerization initiator, an acetophenone such as diethoxy acetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-monophorino (4-thiomethylphenyl) propan-1-one, or the like; a benzoin ether such as benzoin methylether, benzoin ethylether, benzoin isopropylether, benzoin isobutylether, or the like; a benzophenone such as benzophenone, o-benzoyl methyl benzoate, 4-phenyl benzophenone, 4-benzoyl-4xe2x80x2-methyl-diphenyl sulfide, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy) ethyl]benzene methanaminuim bromide, (4-benzoylbenzyl) trimethyl ammonium chloride, or the like; a thioxanthone such as 2,4-diethyl thioxanthone, 1-chloro-4-dichloro thioxanthone, or the like; 2,4,6-trimethylbenzoyl diphenylbenzoyl oxide, or the like; can be mentioned. These can be employed alone or in combination. In addition, as an accelerator (sensitizer), an amine-type compound such as N,N-dimethyl paratoluidine, 4,4xe2x80x2-diethylamino benzophenone, or the like, can be employed in combination. The content of the photopolymerization initiator is preferably in an amount of 0.1 to 10.0% by weight to the radiation curable resin. If the content is not in this range, UV-curing is insufficient.
The volumetric shrinkage ratio associated with the curing of the hard coat layer employing the above radiation curable resin (calculated by the following method) is preferably 20% or less. With a volumetric shrinkage ratio of 20% or more, in the case of a film-shaped transparent substrate, the film will curl severely, and in the case of a rigid substrate such as a glass or the like, the adhesion between the substrate and the hard coat layer will be reduced.
Volumetric shrinkage ratio:D=(Sxe2x88x92Sxe2x80x2)/Sxc3x97100 
wherein
S: specific gravity before curing
Sxe2x80x2: specific gravity after curing
(Specific gravity is measured by the B method picnometer method of Japanese Industrial Standard K-7112.)
In the hard coat layer according to the present invention, a stabilizer (a thermal polymerization inhibitor) for the radiation curable resin such as hydroquinone, p-benzoquinone, t-butylhydroquinone, etc., may be added. It is preferred that the stabilizer be employed in a range of 0.1 to 5.0% by weight to the radiation curable resin.
As a thermosetting resin which can be used in the hard coat layer, phenol resin, furan resin, xylene-formaldehyde resin, ketone-formaldehyde resin, urea resin, melamine resin, aniline resin, alkyd resin, unsaturated polyester resin, epoxy resin, etc., can be employed. These may be employed alone or in combination. In the case in which a transparent substrate consists of plastics, the heat curing temperature cannot be set at a high temperature. In particular, in the case in which PET or TAC is employed, a thermosetting resin which can be cured at 100xc2x0 C. or less is desirably employed.
It is preferable that the curable resin employed in the hard coat layer have a higher transparency. The light permeability (Japanese Industrial Standard C-6714) is preferably 80% or more, and more preferably 90% or more, similarly in the case of the transparent substrate. In the anti-reflective property of the anti-static anti-reflective film according to the present invention, the refractive index of the hard coat layer is preferably in a range of 1.45 to 1.70, and more preferably in a range of 1.5 to 1.65. The refractive index of the hard coat layer can be adjusted by adding high refractive index materials.
As a high refractive index material, a resin including an aromatic ring or a halogen element such as Br, I, Cl, etc., such as a styrol plastic such polystyrene, etc., PET, polycarbonate of bisphenol A, polyvinyl chloride, polytetrabromobisphenol A glycidyl ether, etc., and a resin including S, N, P, etc., such as polyvinyl pyridine, polybisphenol S glycidyl ether, or the like can be recited. Additionally, as another high refractive index material, an inorganic compound fine particle of TiO2 (refractive index: n=2.3 to 2.7), CeO2 (n=1.95), ZnO (n=1.9), Sb2O5 (n=1.71), SnO2 (n=1.95), ITO (n=1.95), Y2O3(n=1.87), La2O3 (n=1.95), ZrO2 (n=2.05), Al2O3 (n=1.63), HfO2 (n=200), Ta2O5, or the like can be recited. These may be employed alone or in combination.
In the present invention, as a method for forming a hard coat layer, directly or via another layer, on one surface of the transparent substrate, there can be mentioned a method consisting of the steps of: mixing appropriately fillers such as crosslinked acryl beads, etc., and water or organic solvent in the resin for forming a hard coat layer described above as necessary; dispersing the mixture using a paint shaker, sand mill, pearl mill, ball mill, attritor, roll mill, high-speed impeller disperser, jet mill, high-speed impact mill, ultrasonic disperser, or the like, to form a coating material or an ink; providing one layer on one surface of the transparent substrate by means of a printing method such as a letterpress printing method such as a flexographic printing method or the like, an intaglio printing method such as a direct gravure printing method, offset gravure printing method, or the like, a planographic printing method such as an offset printing method or the like, a stencil printing method such as a screen process printing method or the like, or a coating method such as an air doctor coating method, blade coating method, knife coating method, reverse coating method, transfer roll coating method, gravure roll coating method, kiss coating method, cast coating method, spray coating method, slot orifice coating method, calender coating method, electrodeposition coating method, dip coating method, die coating method or the like; thermal-drying the coating or printing layers in the case where a solvent is included; and curing the coating or printing layers by means of radiation (in the case of UV radiation, a photo-polymerization initiator is necessary). In the case where the radiation is an electron beam, an electron beam having an energy of 50 KeV to 1000 KeV emitted from various electron beam accelerators such as a Cockroft-Walton apparatus, Van de Graff apparatus, resonance transformer apparatus, insulating core transformer apparatus, linear type apparatus, dynamitron type apparatus, high-frequency type apparatus, or the like may be employed. In the case where the radiation is UV radiation, the UV radiation emitted from the light of an extra-high pressure mercury vapor lamp, high pressure mercury vapor lamp, low pressure mercury vapor lamp, carbon arc lamp, xenon arc lamp, metal halide lamp, or the like can be employed.
In order to improve the coating aptitude or printing aptitude of a coating material or an ink, a levelling agent such as silicone oil or the like, fats and oils such as polyethylene wax, carnauba wax, higher alcohols, bisamide, higher fatty acids, or the like, a curing agent such as isocyanate or the like, an additive such as ultra-microparticles having a particle size of 0.1 xcexcm or less, such as those of calcium carbonate, synthetic mica, or the like, can be employed, as necessary.
The thickness of the hard coat layer is preferably in a range of 0.5 to 10 xcexcm, and more preferably in a range of 1 to 5 xcexcm. In the case where the thickness of the hard coat layer is less than 0.5 xcexcm, abrasion resistance of the hard coat layer is degraded, or in the case of a UV-curable resin being employed in the hard coat layer, the resin fails to cure due to oxidation inhibition. In contrast, in the case where the thickness of the hard coat layer is more than 10 xcexcm, curling occurs due to curing-shrinkage of the resin, microcracking occurs in the hard coat layer, or the adhesion between the transparent substrate and the hard coat layer is decreased.
{circle around (2)} Anti-glare Layer
As an aspect of the present invention, an anti-glare layer may be further provided between the substrate and the low reflective layer. The anti-glare layer is formed by containing a filler in a resin generally used as a binding agent, preferably the above resin for forming a hard coat layer (in this case, the layer is a hard coat anti-glare layer). The light is scattered or diffused by roughening the surface thereof, and thereby the anti-glare effects can be obtained. As the filler, there can be mentioned an inorganic white pigment such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, titanium dioxide, or the like, or an organic transparent or white pigment such as an acrylic resin, polystyrene resin, polyethylene resin, epoxy resin, silicone resin, or the like. In particular, an organic filler which is spheroidal and does not exhibit oil absorbing properties is preferable. By means of employing spheroidal fillers, the projecting parts projecting from the surface of the anti-glare layer are moderated, and contaminants such as oil do not adhere well, and in addition, it is easy to wipe off adhering contaminants.
The filler is preferably present in an amount of 0.5 to 30% in total solid ratio of the anti-glare layer. In particular, it is more preferably present in a range of 1 to 15%. With 0.5% or less of the filler, sufficient anti-reflection effects cannot be obtained. On the other hand, with 30% or more of the filler, not only are the transparency and the contrast of the image degraded, but also durability such as abrasion resistance, environmental resistance, and the like is impaired. In addition, the refractive index of the filler (B method according to Japanese Industrial Standard K-7142) is preferably equivalent to that of the curable resin. In the case where the refractive index of the filler is different from that of the curable resin, light is scattered at the interface of the resin and the filler, and therefore the transparency is impaired. As an example of fillers having a refractive index equivalent to that of the curable resin, there can be mentioned organic fillers, and in particular crosslinked acryl beads.
As the crosslinked acryl beads, those consisting of polymers and copolymers obtained by means of polymerization, such as suspension polymerization, using an acrylic monomer, such as acrylic acid and an ester thereof, methacrylic acid and an ester thereof, acrylic amide, acrylonitrile, or the like, a polymerization initiator such as persulfuric acid, or the like, and a crosslinking agent such as ethylene glycol dimethacrylate, or the like, is preferably employed. In particular, as an acrylic monomer, a monomer using methyl methacrylate is preferred. The crosslinked acrylic beads thus obtained are spheroidal and do not exhibit oil absorbing characteristics. For this reason, in the case where the beads are employed in the anti-glare layer, excellent stain resistance can be exhibited. In addition, the crosslinked acrylic beads may be surface-treated by fats and oils, a silane-coupling agent, an organic or inorganic material such as a metal oxide, or the like in order to improve dispensability of the coating material.
The anti-glare layer according to the present invention can be provided by the same manner as the above laminating method of the hard coat layer.
In the anti-static anti-reflective film according to the present invention produced by the above process, the HAZE value according to Japanese Industrial Standard K-7105 is preferably in a range of 3 to 30, and more preferably in a range of 5 to 15. With a HAZE value of less than 3, the light scattering effects are small, and therefore sufficient anti-reflection effects cannot be obtained. On the other hand, with a HAZE value of more than 30, the image contrast is degraded and visibility is degraded, and for these reasons, it is not preferred since an inferior display will result. The HAZE value is a clouding value, and it is calculated according to the following expression by measuring a luminous diffuse transmittance (Td %) and a total light transmittance (Tt %) using an integrating sphere type light transmittance measuring apparatus.
HAZE value=Td/Ttxc3x97100 